Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). A long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
To increase the capacity for the users' demand of services, increasing the bandwidth may be essential, a carrier aggregation (CA) technology or resource aggregation over intra-node carriers or inter-node carriers aiming at obtaining an effect, as if a logically wider band is used, by grouping a plurality of physically non-continuous bands in a frequency domain has been developed to effectively use fragmented small bands. In CA, two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A user equipment (UE) may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. A Rel-10 UE with reception and/or transmission capabilities for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells. A Rel-8/9 UE can receive on a single CC and transmit on a single CC corresponding to one serving cell only.
In 3GPP LTE Rel-12, a new study on small cell enhancement has started, where dual connectivity is supported. Dual connectivity is an operation where a given UE consumes radio resources provided by at least two different network points (master eNB (MeNB) and secondary eNB (SeNB)) connected with non-ideal backhaul while in RRC_CONNECTED. Furthermore, each eNB involved in dual connectivity for a UE may assume different roles. Those roles do not necessarily depend on the eNB's power class and can vary among UEs.
The synchronization requirement for a home eNB (HeNB) is defined as the difference in radio frame start timing, measured at the transmit antenna connectors, between the HeNB and any other HeNB or eNB which has overlapping coverage. The synchronization requirement shall be set to 3 us in all cases, except when the HeNB gets its synchronization when performing network listening off cells with propagation distance greater than. This requirement shall apply independent of the synchronization technique used (global positioning system (GPS), institute of electrical and electronics engineers (IEEE) 1588v2, network listening). In scenarios where synchronization is obtained via network listening off cells with propagation distance greater than, the synchronization requirement shall be 1.33 us plus the propagation delay between the HeNB and the cell selected as the network listening synchronization source (e.g., when the propagation distance is, the synchronization requirement is 10 us). In terms of the network listening synchronization source selection, the best accurate synchronization source to global navigation satellite system (GNSS) should be selected.
Network listening is a useful technique which can be utilized when other techniques such as global positioning system (GPS) or institute of electrical and electronics engineers (IEEE) 1588v2 are not available. Some enhancements to support efficient network listening mechanisms may be required.